This invention relates to plant diseases and deleterious microorganisms found in environments adapted for the growth of higher order plants, and more particularly to control and inhibition of plant diseases and deleterious microorganisms found in such environments.
In environments adapted for the growth of plants of higher biological development or complexity than microorganisms such as bacteria, yeast, algae or simple fungus, that is, in environments adapted for the growth of higher order plants, development of such microorganisms on practically any moist surface has been a longstanding and intractable problem.
Greenhouses contain a myriad of water sources, including irrigation water, irrigation water run-off, spilled water, cleaning water, condensation, atomized water drifting from a humidifier or evaporative cooler and extraneous sprayed water as might result from a water hose. Since almost all surfaces in a greenhouse tend to become moist from these sources, nearly any surface in a greenhouse may serve as a site for microorganism growth. Thus, in conventional greenhouses, microorganisms inevitably colonize and grow not only on the plants themselves, but also on all other surfaces such as walls, ceilings, floors, flower pots, flats, irrigation mats, irrigation equipment and evaporative cooling pads.
Similarly, in outdoor nurseries, crop fields, and any other environment, such as lawns or golf courses, adapted for the growth of higher order plants, microorganisms tend to develop on irrigation or sprinkling equipment, soil and the plants themselves, and containers and planters.
Growth of microorganisms often is deleterious to the operation of an irrigation system as well as to the higher order plants themselves. Growth of slime bacteria has a propensity to foul the system and clog irrigation equipment, reducing its efficiency. Likewise, development of yeast, fungus and algae causes spoiling of plants, and the fruits and seeds of plants, and otherwise harms higher order plants. Development of pathogenic microorganisms such as Verticillium, Pythium, Fusarium, and Pseudomonas in or on plants also causes various plant diseases. Furthermore, microorganism development in living plants may accelerate rotting or spoiling of the plants after harvesting, or even accelerate rotting or spoiling of fruits or seeds harvested from the plants. Moreover, development of microorganisms in a greenhouse can cover the greenhouse with an unappealing slime which rubs off on workers who brush against a coated greenhouse surface, blocks light transmission through the glass walls of the greenhouse, fouls the greenhouse, makes the greenhouse floors slippery, provide a breeding ground for fungus gnats and other pests, and potentially poses health hazards.
Previous attempts to inhibit microorganism development in plant environments either have failed or have been self-defeating because ordinary biocides or disinfectants, such as bleach or various quaternary ammonium compounds, that have been employed to kill or inhibit microorganisms, also are toxic to the higher order plants in the environment. Thus, ordinarily the cleaning of greenhouse surfaces has entailed tedious, labor intensive careful scrubbing of the surfaces to avoid accidentally contacting a plant with the biocide, or time consuming removal of all the higher order plants from the greenhouse before washing down the surfaces with a hose. Moreover, it seems clear that because such biocides are phytotoxic, they cannot be considered for direct plant treatment either in the irrigation water to keep clean the surfaces contacted by the water, or in irrigation water or otherwise in order to treat the plants themselves. On the other hand, however, while some biocides may have low enough phytotoxic characteristics to use directly on plants, many have been associated with health hazards to humans that eat the plants or harvested parts thereof.
In addition to the health hazards from the toxicity of the oxidizing biocides used in the prior art for treating microorganism development around plants, such biocides also usually involve other health hazards from some other characteristic, such as the explosiveness of chlorine gas tanks. Other problems with many of the conventional chlorine biocides include instability of the biocide in the presence of organic matter, effectiveness of the biocide only in a narrow pH range, and the formation of chloramines in the presence of ammonia, thereby producing residual compounds which undesireably persist in the environment. Further, the additives typically employed in irrigation systems for control of certain microorganisms, or for other purposes such as fertilization, tend to be compositions of high water solubility and so require employment of expensive pumps and other mechanical parts to regulate the concentration of the additives, to maintain an appropriate concentration and to avoid a phytotoxic overdose.
As disclosed in Paterson U.S. Pat. No. 3,412,021 and Macchiarolo U.S. Pat. No.4,297,224, 1-bromo-3- chloro-5,5-dimethylhydantoin is known as an oxidizing biocide for use in water treatment in certain environments, such as swimming pools and cooling towers in which higher order plants are not a concern. Patent and other technical literature discloses a number of uses for this and other N-halohydantoin compounds based on the biocidal properties of these compounds.